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Published June 2018 | Published + Supplemental Material
Journal Article Open

Deep-biosphere methane production stimulated by geofluids in the Nankai accretionary complex

Abstract

Microbial life inhabiting subseafloor sediments plays an important role in Earth's carbon cycle. However, the impact of geodynamic processes on the distributions and carbon-cycling activities of subseafloor life remains poorly constrained. We explore a submarine mud volcano of the Nankai accretionary complex by drilling down to 200 m below the summit. Stable isotopic compositions of water and carbon compounds, including clumped methane isotopologues, suggest that ~90% of methane is microbially produced at 16° to 30°C and 300 to 900 m below seafloor, corresponding to the basin bottom, where fluids in the accretionary prism are supplied via megasplay faults. Radiotracer experiments showed that relatively small microbial populations in deep mud volcano sediments (10^2 to 10^3 cells cm^(−3)) include highly active hydrogenotrophic methanogens and acetogens. Our findings indicate that subduction-associated fluid migration has stimulated microbial activity in the mud reservoir and that mud volcanoes may contribute more substantially to the methane budget than previously estimated.

Additional Information

© 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial license, which permits use, distribution, and reproduction in any medium, so long as the resultant use is not for commercial advantage and provided the original work is properly cited. Received for publication July 24, 2017. Accepted for publication May 1, 2018. We thank all crews, drilling team members, and technical staffs on the deep-sea drilling vessel Chikyu and the research vessel Hakuhomaru for support with core sampling from KMV#5 during JAMSTEC Chikyu Expeditions 903, 906, and KH06-04 cruises. We are also grateful to IODP for providing sediment core samples from Site C0002 during Expedition 315. We are grateful to S. Fukunaga, S. Hashimoto, K. Iijima, A. Imajo, H. Machiyama, Y. Nishio, S. Tanaka, H. Tomiyama, and N. Xiao for useful discussions and/or technical assistance. This is a contribution to the Deep Carbon Observatory. This study was supported, in part, by the Japan Society for the Promotion of Science (JSPS) Strategic Fund for Strengthening Leading-Edge Research and Development (to JAMSTEC and F.I.), the JSPS Funding Program for Next Generation World-Leading Researchers (GR102 to F.I.), the Grant-in-Aid for Science Research (nos. 23681007, 26287128, and 17H01871 to A.I.; no. 26251041 to F.I.; no. 17H06105 to N.Y.), and the East Asia and Pacific Summer Institutes program through the NSF and JSPS (no. 1308171 to D.H.C.). Lipid analyses by M.Y.Y. and shipboard work by F.S. were financed by the European Research Council under the European Union's Seventh Framework Programme—"Ideas" Specific Programme (no. 247153 to K.-U.H.). Author contributions: A.I. and F.I. designed the study. F.I. led the project as the chief scientist of JAMSTEC Chikyu Expeditions 903 and 906. Y.K. coordinated Expeditions 903 and 906 as the expedition project manager. A.I., F.I., R.R.A., T.H., Y.M., T. Toki, G.L.A., J.A., D.H.C., T.F., Y.I., H.I., J.K., H.K., K.-i.N., Y.N., M.N., H.R., S.S., F.S., A.T., W.T., T. Terada, H.T., and Y.T.Y. collected and analyzed the sediment core samples and data as shipboard scientists. S.H., S.K., Y.O., S.O., K.T., D.T.W., M.Y.Y., K.-U.H., M.I., M.A.L., S.M., V.J.O., T. Tuji, U.T., and N.Y. analyzed the samples and data as shore-based scientists. A.I. and F.I. cowrote the manuscript. All authors discussed the results and commented on the manuscript. The authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. The 16S rRNA gene sequences in this study were all deposited in the DNA Data Bank of Japan/European Molecular Biology Laboratory/GenBank nucleotide sequence databases under accession no. DRA001034. The 16S rRNA gene sequence of strain 1H1 was also available under accession no. LC170394. Strain 1H1 has been deposited in the Japan Collection of Microorganisms (JCM 19936). Additional data related to this paper may be requested from the authors.

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August 22, 2023
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